Pulsed ion beam measurement of defect diffusion lengths in irradiated solids.

Radiation-generated point defects in solids often experience dynamic annealing-diffusion and interaction processes after the thermalization of collision cascades. The length scale of dynamic annealing can be described in terms of the characteristic defect diffusion length (Ld). Here, we propose to measure Ld by a pulsed beam method. Our approach is based on the observation of enhanced defect production when, for individual ion pulses, the average separation between adjacent damage regions is smaller than Ld. We obtain a value for Ld of ~30 nm for float-zone Si crystals bombarded at room temperature with 500 keV Ar ions.

Pulsed ion beam measurement of the time constant of dynamic annealing in Si.

Under ion irradiation, all crystalline materials display some degree of dynamic annealing when defects experience evolution after the thermalization of collision cascades. The exact time scales of such defect relaxation processes are, however, unknown even for Si at room temperature. Here, we use a pulsed ion-beam method to measure a characteristic time constant of dominant dynamic annealing processes of about 6 ms in Si bombarded at room temperature with 500 keV Ar ions.

The "differential diagnosis" for multiple diseases: comparison with the binary-truth state experiment in two empirical studies.

RATIONALE AND OBJECTIVES: In practice readers must often choose between multiple diagnoses. For assessing reader accuracy in these settings. Obuchowski et al have proposed the "differential diagnosis" method, which derives all pairwise estimates of accuracy for the various diagnoses, along with summary measures of accuracy. The current study assessed the correspondence between the differential diagnosis method and conventional binary-truth state experiments. MATERIALS AND METHODS: Two empirical studies were conducted at two institutions with different readers and diagnostic tests. Readers used the differential diagnosis format to interpret a set of cases. In subsequent readings they interpreted the cases in binary-truth state experiments. Spearman rank correlation coefficients and the percentages of agreement in scores were computed, and the areas under the receiver operating characteristic curves were estimated and compared. RESULTS: The between-format Spearman rank correlation coefficients were 0.697-0.718 and 0.750-0.780 for the two studies; the between-reader correlations were 0.417 and 0.792, respectively. The percentages of agreement between formats for the two studies were 50.0%-51.7% and 72.9%-78.8%; the percentages of agreement between readers were 45.0% and 80%, respectively. In the first study there were several significant differences in the areas under receiver operating characteristic curves; in the second study these differences were small. CONCLUSION: The differences observed between the two formats can be attributed to within-reader variability and inherent differences in the questions posed to readers in the multiple-diagnoses versus binary-truth state reading sessions. The differential diagnosis format is useful for estimating accuracy when there are multiple possible diagnoses.

Unenhanced helical CT in the evaluation of the urinary tract in children and young adults following urinary tract reconstruction: comparison with sonography.

PURPOSE: To compare the accuracy of unenhanced, helical CT with sonography for the detection of complications of urinary tract reconstruction. MATERIALS AND METHODS: Forty-six kidneys in 24 patients were examined with CT and sonography. All scans were assessed for ease of renal visualization, presence of renal, ureteral, and bladder calculi, renal scars, hydronephrosis, and abdominal wall hernia. The results of both imaging modalities were independently reported. RESULTS: CT provided excellent visualization of all 46 kidneys, while sonography provided poor visualization of 8 kidneys (17%) (P < 0.001). CT detected calculi in 10 kidneys, 1 ureter, and 7 bladders. Sonography detected calculi in only 2 kidneys, and 2 bladders. Overall, CT detected significantly more calculi than US (18 vs 4, P = 0.01). CT detected scarring in 15 kidneys, while sonography detected scarring in 10. Hydronephrosis was detected in 6 kidneys by CT and in 8 kidneys by sonography. Three abdominal wall hernias were seen at CT that were not seen at sonography. CONCLUSION: CT is superior to sonography for the detection of urinary tract calculi and renal scarring. CT will demonstrate abdominal wall hernias that are unsuspected.

Using helical CT to diagnosis acute appendicitis in children: spectrum of findings.

Helical CT in children shows an overlapping and wide spectrum of appearances of the normal and acutely inflamed appendix. The normal appendix may measure up to 10 mm in maximal diameter but should not have other CT signs of acute inflammation.

Imaging evaluation of suspected appendicitis in a pediatric population: effectiveness of sonography versus CT.

OBJECTIVE: The purpose of this study was to compare the diagnostic accuracy of graded compression sonography with that of helical CT for the diagnosis of appendicitis in a pediatric and young adult population. SUBJECTS AND METHODS: Between June 1996 and April 1999, 386 pediatric and young adult patients with suspected appendicitis were examined using sonography, CT, or both: 233 underwent sonography only, 71 underwent CT only, and 82 underwent sonography and CT. All sonograms and CT scans were prospectively interpreted as showing positive or negative findings for appendicitis by one of six pediatric radiologists. CT and sonographic findings were correlated with surgical and histopathologic findings or findings at clinical follow-up. RESULTS: Helical CT had a significantly higher sensitivity (95% versus 78%, p = 0.009) and accuracy (94% versus 89%, p = 0.05) than graded compression sonography for the diagnosis of appendicitis in children, adolescents, and young adults. The specificity of both techniques was 93%. Twenty of 82 patients who underwent both sonography and CT had discordance between the findings of the two examinations. The CT results were correct in a significantly greater number of patients with discordant examinations (17/20 patients [85%]). CONCLUSION: Helical CT has a significantly higher sensitivity and accuracy than graded compression sonography for the diagnosis of appendicitis in a pediatric and young adult population, particularly in children more than 10 years old.

Evaluation of suspected appendicitis in children and young adults: helical CT.

PURPOSE: To evaluate the accuracy of helical computed tomography (CT) for the diagnosis of appendicitis in children and to assess the utility of CT in establishing alternative diagnoses. MATERIALS AND METHODS: The medical records of 154 children (median age, 12 years; age range, 1-20 years) who were suspected to have appendicitis and who underwent CT were reviewed. The gastrointestinal tract was opacified in 151 of 154 patients: Only orally administered contrast material was used in 126 patients; only rectally administered contrast material, in 21 patients; and both oral and rectal contrast material, in four patients. CT findings were correlated with surgical and histopathologic findings or with clinical follow-up findings. RESULTS: Sixty-four CT scans were interpreted as positive for appendicitis and included 58 true-positive and six false-positive scans. Ninety scans were interpreted as negative and included 87 true-negative and three false-negative scans. CT had a sensitivity of 95% and a specificity of 94% for the diagnosis of appendicitis. In addition, in 32 (34%) of 93 patients without appendicitis, an alternative diagnosis was established on the basis of CT findings. CONCLUSION: Helical CT is useful in a pediatric population to diagnose or exclude appendicitis and to establish an alternative diagnosis.

Foraging under the risk of cannibalism leads to divergence in body size among tiger salamander larvae.

Populations of plants and animals are almost always made up of individuals of different sizes. In populations where cannibalism is common, this size variation can influence rates of mortality and growth and affect population regulation. Size variation can be caused by a variety of mechanisms. One of these is due to size-specific responses to the threat of predation by potentially cannibalistic conspecifics. We investigated the role of anti-predator behavior in size structure development within single-aged cohorts of Arizona tiger salamander larvae. In a laboratory experiment, we show that size variation increases over time within groups of salamanders, even if they are fed in isolation. We also show that increasing the size of neighbors decreases the feeding rate of small salamander larvae. However, increasing density of neighbors did not have a significant effect on feeding rate. These results are consistent with the hypothesis that size variation among tiger salamander larvae is, in part, a result of size-specific responses to predation risk. We discuss the potential for feedback between size structure development, predation risk, and rates of cannibalism.

Imaging the child with a limp.

A great many pathologic conditions can cause a child to limp. Prior to imaging, it is necessary to complete a thorough history and physical examination in order to limit the differential diagnosis to a few possible causes. The selection of imaging modalities should then be guided by the history and physical examination findings. Because of their sensitivity and specificity for detecting a wide range of bone pathology, radiographs should be obtained first. Plain radiographs often are diagnostic. The choice of sonography, CT, bone scintigraphy, or MR imaging is made while keeping in mind the strengths of each imaging modality.

MR imaging of hip disorders.

Magnetic resonance (MR) imaging has been applied to the study of a variety of hip disorders, principally the evaluation of avascular necrosis. The authors reviewed their experience with MR imaging of a variety of pediatric and adult hip diseases. Attention to the details of the imaging technique is essential for maximizing the diagnostic potential of MR imaging in the work-up of hip disease. Specific protocols that incorporate surface coil imaging, oblique imaging planes, and alternative pulse sequences are the foundation of successful hip studies. Gradient-echo imaging is essential for evaluating cartilaginous disorders, particularly in pediatric patients. For patients to benefit from the diagnostic capabilities of MR imaging, an appreciation of the unique information it provides must be communicated to referring physicians. In addition, an awareness of the atypical and unique MR appearances of certain hip disorders is necessary for accurate interpretation.

Evidence of multifactorial mechanisms in an adriamycin-resistant HL-60 promyelocytic leukemia cell line.

HL-60/AR leukemia cells, which were 60-fold resistant to the growth inhibitory activity of adriamycin, remained sensitive to the antiproliferative and differentiation-inducing activities of aclacinomycin A. The replication of HL-60/AR and of adriamycin sensitive parental HL-60 cells was inhibited by greater than 80% by 30 nM aclacinomycin A and the majority of cells (about 60 to 70%) of each line underwent granulocytic differentiation when treated with this agent, as assessed by the reduction of nitroblue tetrazolium. Measurement of the initial rates of uptake of daunorubicin and steady-state levels of adriamycin in sensitive and resistant lines indicated that transport differences do not fully account for the insensitivity of HL-60/AR cells to these anthracyclines. Furthermore, 30-fold greater levels of cell-associated adriamycin were required in HL-60/AR cells for toxic effects equivalent to those occurring in parental HL-60 cells. Analysis of DNA histograms of adriamycin treated HL-60 cells indicated that cell-cycle progression was blocked in G2-M, while this antibiotic blocked progression of resistant HL-60/AR cells in the S phase. These results suggest that, in addition to alterations in membrane permeability, differential sensitivity of multiple biochemical targets may be important in the toxicity and the development of resistance to anthracyclines. Furthermore, the finding that HL-60/AR cells do not exhibit cross-resistance to aclacinomycin A indicates that this oligosaccharide-containing anthracycline may have utility in the treatment of adriamycin resistant neoplasms.